Biological Aspects of Hybrid Poplar Cultivation on Floodplains in Western North America
Biological Aspects of Hybrid Poplar Cultivation on Floodplains in Western North America (48pp. 1.2MB About PDF)
Abstract
Fast-growing hybrid poplars--the product of selective breeding of native cottonwoods-- are being widely planted to supplement the diminishing supply of natural hardwoods. As effective biofilters, these trees are also being increasingly used to treat agricultural runoff and municipal wastewaters. Given such uses, the cultivation of hybrid poplars in floodplain habitats is expected to increase in the coming years. This report discusses the major biological distinctions between hybrid poplars and native cottonwoods, and explores some of the potential management issues associated with their cultivation near riparian corridors.
The biological differences between hybrid poplars and native cottonwoods are subtle, with varying levels of ecological significance. Such differences arise in the following areas: a) genetic and reproductive properties, b) growth and water-use characteristics, and c) wildlife habitat values. Much of our current knowledge of these factors is derived from comparative studies of parental (native cottonwoods) and hybrid genotypes (F 1 , F 2 , and backcrosses). Only a limited number of studies have compared the ecological properties of commercial poplar plantations with native habitats, hence the potential outcome of ecological interactions must often be inferred.
Over the years, widespread planting of non-native poplars in the West has had a limited effect upon the genetics and ecology of native riparian cottonwoods. Restricted levels of gene exchange are related to phenological incompatibilities and the reduced pollen and seed viability of hybrid crosses. Although hybrid poplars are noted for rapid growth, their potential impact on groundwater and streamflows is comparable to slightly lower than other agricultural crops. Hybrids are more drought tolerant than native cottonwoods, yet potentially more vulnerable to flooding. These physiological differences may favor hybrids in some riparian settings. Since commercial plantations are not designed to serve as wildlife habitat, lower habitat values relative to native riparian zones are expected.
However, their habitat values are greater than traditional row and pasture crops. Given our current knowledge, numerous research and management opportunities exist for reducing gene exchange and improving the habitat properties of hybrid poplar plantations. Future research needs to focus upon these opportunities, while also promoting the conservation and study of native riparian cottonwood ecosystems.